A Multi-hop network is a collection of wireless mobile computing nodes dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration. Multi-hop networks include packet-radio networks, ad-hoc networks, and sensor networks. As network size grows, communication between two nodes may go through multiple wireless links, or through multiple “hops” for one node to exchange data with another node across the wireless network. This multi-hop aspect occurs for a number of different reasons, for example, because of limited transmission range of wireless devices, communication path obstacles, spatial spectrum reuse, power saving considerations (the lifetime of a network that is operating on battery power is limited by the capacity of its energy source), and so on.
Unlike wired networks that typically have fixed network topology (except in case of node failures), real-time physical displacement, or mobility of network nodes in a multi-hop network is common because of the nature of the applications multi-hop networks are designed to support (e.g., applications for disaster recovery, battlefield, search and rescue, sensor nets, and so on). Because of node mobility, each node in a wireless network may change network topology by adjusting transmission power to control the set of one-hop neighbors, or nodes that are in communication with the node. Multi-hopping combined with a large network size, node mobility, device heterogeneity, bandwidth limitations, and battery power limitations make wireless multi-hop network topology control a major challenge.
The primary goal of topology control is to design power efficient algorithms that maintain network connectivity and optimize performance metrics such as network lifetime and throughput. Conventional techniques to provide wireless distributed multi-hop network topology control typically require positional information such as positional information that is acquired from a Global Positioning System (GPS) implementation at each node in the network. This positional information requirement for topology control is problematic for a number of reasons.
Even in an ideal environment acquisition of positional information may take a substantial amount of time—negatively impacting network response time and throughput. The actual amount of time that it takes to acquire positional information typically depends on how quickly each respective node can establish communication with multiple satellites and exchange data with the satellites to obtain corresponding positional data. Thus, respective nodes in the network may have to wait for an indeterminate, and potentially infinite amount of time before receiving positional information. This is because positional information can only be reliably acquired in a limited number of environments.
Certain environments can completely block or substantially hamper satellite signals to nodes in a wireless multi-hop network. For instance, GPS signals are often undetectable or sporadic in indoor environments, in cloudy weather, in heavily treed areas, in cities, and so on. At best a node in such in environment will be able to obtain its required positional information. However, such environments often make communications between a node and the satellites irregular, which may cause a node to fade in and out of the network topology. At worst, a node may never receive its required positional information because it is blocked by environmental conditions that make satellite signal communication with network nodes impossible. In this worst case scenario, a node may become completely superfluous with respect to its role in the network.
Yet another problem, for example, with requiring positional information at each node in a multi-hop network to provide topology control is that technology required to acquire positional information is relatively expensive. Requiring such technology at each node in the network can substantially increase implementation costs of wireless multi-hop networks as well as corresponding maintenance costs.
Accordingly, the following described subject matter addresses these and other problems associated with providing distributed topology control for multi-hop wireless networks.